Chromium-steel alloy



UNITED STATES PATENT ()FFIOE.

JOHN L. COX, F PHILADELPHIA, PENNSYLVANIA, ASSIGNOR TO MIDVALE STEEL & ORDNANCE COMPANY, OF PHILADELPHIA, PENNSYLVANIA. A CORPORATION OF DELAWARE.

CHROMIUM-STEEL ALLOY.

1W0 Drawing.

To all whom it may concern:

. Be it known that I, JOHN L. Cox, a citizen of the United States, residing at Philadelphia, county of Philadelphia, and State of Pennsylvania, have invented a 'new and useful Improvement in Chromium Steel Alloy, of which the following is a full, clear, and exact description.

- The production of high chromium steel adapted to take a high polish and resist corrosion and to take and retain a cutting edge is well known. Such an alloy is especially adapted to the manufacture of cutlery and some of it makes an "excellent non-deforming tool steel.

It has heretofore been supposed. by most metallurgists. that the percentage of carbon in such an alloy must be maintained relatively low. One patent places the upper limit of eflic-iency at .7 per cent. carbon with a preferential proportion of about .3 per cent. Another patent prescribes a wider range of from .1 to 1.0 per cent. Another patent, however, prescribes a relatively high carbon range of from 1. to 1.50 per cent. and states that for special uses the proportion of chromium may reach as high as 20 per cent, but in this patent the prescribed workable range of chromium is between and per cent. Still another patent describes an alloy consisting of chromium from 20 to 35 per cent, preferably from to per cent.. but prescribes that the carbon content shall be from 1.5 to 3. per cent. Laboratory experimenters have tested qferrous alloys having various percentages of chromium and carbon and havingusually. also. substantial percentages of other ingredients, without. however. arriving at any useful discovery of the superiority of any specific composition 01' the special availability of any specific composition for any particular use.

I have ascertained that in the manufacture of high carbon chromium alloy steels no imperative reason exists for restricting the percentage of chromium to below 9.0 per cent., which is the highest permissible percentage recognized by three of the above patents; but that, on the other hand. if the percentage of chromium be increased beyond twenty per cent, the percentage of carbon should be increased accordingly, but not Specification of Letters Patent.

.Iatented Mar. 16, 1920.

to the degree specified by the fourth patent mentioned. For example if the percentage of chromiumibe just above twenty per cent. the percentage of carbon should not much exceed one per cent. it-h the highestpracticable percentage of chromium the percentage of carbon should be less than the minimum (1.5) prescribed in the last named patent. While it may be possible to manufacture a serviceable chromium steel adapted for cutlery and having the property of resisting tarnishing and remaining bright. in which the percentage of carbon exceeds 1.5 per cent. the percentage ofchromium. in such high carbon steel, nmst be raised so high that not only is the alloy relatively eX- pensive but it becomes diflicult to forge and impossible to roll to the thin sections required for cutlery.

I have made an excellent non-tarnishing cutlery steel having a carbon content of 1.15 per cent. and a chromium content of 23 per cent. should not reach 1.5 per cent, and while the percentage of chromium is preferably not over 30 per cent, or thereabouts. it may be. without advantage. increased considerably beyond this percentage.

For some purposes a clnomium-stcel alloy containing between 1.0 and. 1.5 per cent. of carbon. even though the percentage of chromium be relatively high. exhibits no advantage over an alloy containing correspondingly lower percentages of carbon and chromium. For other purposes. the marked tendency of high chromium steels to fail to harden on the surface can best be avoided by increasing the carbon content. while the objections to the higher carbon can be overcome by increasing the chromium content correspondingly.

Thus my discovery presents two aspects: First. that a high grade cutlery and tool chromium-steel alloy of a grade equal to The permissible range of carbon.

alloy, whatever the percentage of chromium in the latter may be.

- cannot be readily'forged and cannotbe read- A typical composition embodying my invention is the following:

Carbon 1. per cent. Chromium 23 per cent. Iron about 75- per cent.

My improved alloy is especially adapted to cutting purposes, as in the manufacture of machine tools for cutting metals and for table cutlery. It resists tarnishing, may be readily forged in the lower ranges, assumes a high degree'of hardness on heating and quenching, and is readily softened by appropriate drawing methods.

Vhile' the ratio of carbon tochromium need not be invariable, inasmuch as a con- .siderable excess of chromium is un'objection- 'able when the alloy 1s lntended for cert-am .mentioned, only the two which require a low range of carbon are comparable with my product and I believe my product, in regard to this quality, is appreciably superior to any known composition. These two compositions, however, are not comparable with my composition with respect to the capacity to take and retain a cutting edge. while my composition, in this regard, is at least equal to the third of the compositions hereinbefore referredto. It is, of course, obvious that any composition having so high a carbon range as the fourth composition mentioned ily softened. It will. therefore, be apparent that my product exhibits a very valuable" union of qualities .not heretofore known,

namely: stainlessness, hot malleability and capacity for takingand holding a cutting edge and capacity for being readily softened for machining cold.

Having now fully described my invention,

3. A chromium-steel alloy containing over 1.0 per cent. and less than 1.5 per cent. of Y carbon and in excess of twenty per cent. of chromium wherein the ratio of chromium to carbon is between 15:1 and 1. r

*1. A chromium-steel alloy containing a predominating proportion of iron, carbon over 1.0 per cent. and less than 1.5 per cent. and chromium over 20 per cent, the same being readily forged. assuming a high degree of hardness on heating and quenching. being readily softened by drawing, and adapted to be made into a finished and highly polished cutting instrument resistive of corrosion and adapted to take on and retain a cutting edge. i

5. An article of manufacture, such as cutlery and edged tools. composed of a steel alloy containing over 1.0 per cent. and less than 1.5 per cent. of carbon, over 20 per cent.

of chromium and a preponderating proportion of iron.

6. A chromium steel alloy containing a preponderating proportion of iron. over 1.0 per cent. and less than 1.5 per cent. of carbon and in excess of twentyeper cent. of

chromium, wherein the ratio of ch'romiunr to carbon approximates 20:1.

'4. A chromlum steel alloy containing apreponderating proportion ofiron. over 1.0

per cent. and lessthan 1.5 per cent. of carbon and in excess of twenty per cent. of chromium, wherein the rat-i0 of chromium to carbon is not less than approximately 20: 1.

8. A chromium steel. alloy containing a JOHN L. COX. 

